Wheat cultivation benefits significantly from crop rotation. Maize, chard, tomato, potato, sunflower, soybeans are good cultivation precessions, because wheat is able to use the residue of fertility left in the soil by these crops very well, even better if it is not other cereals. Wheat, however, is not the best crop to use the high fertility left by long-term meadows (legumes and grasses). In arid areas, the succession of wheat to fallow is traditional, where the organic substance of the soil is mineralized and enriched with water. The succession to a renewal crop also allows a less deep tillage, sod seeding or minimum tillage.
The nitrogen content in the soil is often not sufficient to satisfy the cultivation needs, both for the scarce presence and for the delayed response with respect to the needs of the single phenological phases. During the cold months, both mineralization and nitrification processes are practically suspended due to low temperatures (except for rare and temporary occasions of warmth); they will resume in the spring with the heating of the soil, but too late compared to the need for the wheat in the rising phase.
Phosphorus and potassium cannot be washed out as they are adsorbed by the soil and are released into the circulating solution as the crop absorbs them: it is therefore sufficient to integrate the soil, if insufficient, with pre-sowing fertilizations.
During the cold months in which the wheat carries out the long phase of tillage, it can only count on the residual nitric nitrogen of the previous crop, the quantity of which varies according to the organic matter content of the soil, the mineralization rate and the residue of fertilization not used by the previous crop. Furthermore, this small portion of residual nitric nitrogen can be washed away, in whole or in part, by the autumn/winter rains. In conclusion, the soil is a bad supplier of nitrogen for wheat. Considering that this element is the main factor of the quantitative-qualitative yield of wheat and that the supply of nitric nitrogen is scarce and late, it follows that the farmer must intervene with nitrogen fertilizer contributions according to the requirement in each development phase.
Time of fertilization.
Phosphorus and potassium are retained by the soil and have very little mobility. Therefore it is necessary that they are buried up to the depth in which the roots will develop.
The best nitrogen fertilization technique is to distribute the nitrogen not long before the period of use by the crop to minimize the risk of leaching. Therefore abundant fertilization when sowing is not recommended, also given the limited initial needs of the crop and the presumed "old strength" present in the soil.
Only after exploiting crops and/or after burying the straw, an additional supply of 20-40 kg per hectare of nitrogen can be useful at sowing, together with the phosphate fertilizer (Biammonic phosphate 18-46-0).
Apart from the case mentioned above, all nitrogen requirements can be met with top dressing fertilizations: the best technique involves 2-3 fertilizations:
- the first, in the month of January to favor tillering; it could be omitted if the crop is in good development conditions and of an intense green color, otherwise it should be done with 15-20% of the total expected dose (Calcium nitrate);
- the second, indispensable in February, to favor the color change and morphogenesis of the ears, distributing 35-40% of the total (ammonium nitrate);
- the third, fundamental in March, just before the start of the rising, to ensure the satisfaction of the very high needs during the rising: this distributing the remaining share of 45-50% of the total (Urea 46%).